Synthetic resin materials have been used for forming preformed bodies (usually called preforms) that are formed into beverage containers through hollow forming, and for forming container lids and container bodies such as cups. As is well known among people skilled in the art, a composite resin material is often used comprising outer molten resins and at least one inner molten resin layer wrapped in the outer molten resin layers. As the outer molten resin, in many cases, a synthetic resin having excellent mechanical properties and sanitary properties is selected and as the inner molten resin, a synthetic resin having excellent gas-barrier property is selected.
WO2004/065101 discloses an apparatus for feeding a composite molten resin comprising an outermost flow path through which a main layer-forming molten resin flows for forming a main layer of a preform, an outer flow path having an outer discharge port opened in the outermost flow path and through which a sub-layer-forming molten resin flows for forming a sub-layer of the preform, and an inner flow path having an inner discharge port opened in the outer flow path and through which a core-forming molten resin flows for forming a core.
The inner discharge port is provided with opening/closing means for selectively opening and closing the inner discharge port and with intermittent means for intermittently disposing the sub-layer-forming molten resin at the outer discharge port. As the inner discharge port is opened and closed by the opening/closing means of the apparatus for feeding the molten resin, the core layer-forming molten resin flows intermittently into the outermost flow path from the inner flow path through the outer flow path. The core layer-forming molten resin is pressed and deformed by the sub-layer-forming molten resin as the core layer-forming molten resin flows into the inside of the outermost flow path.
JP-B-6-49318 discloses an apparatus for forming a composite molten resin comprising an outer flow path through which a main layer-forming molten resin flows for forming a main layer of a preform, an inner flow path having an inner discharge port opened in the outer flow path and through which a shell layer-forming molten resin flows for forming a shell layer of the preform, and an innermost flow path having an innermost discharge port opened in the inner flow path and through which a core-forming molten resin flows for forming a core layer of the preform.
The innermost discharge port is provided with opening/closing means for selectively opening and closing the innermost discharge port. As the innermost discharge port is opened and closed by the opening/closing means, the shell layer-forming molten resin is fed into the outer molten resin so as to cover the core layer-forming molten resin like a shell.
Usually, the main layer and the sub-layer which use the same material can be regarded to forming one layer. The preform formed by the technology of WO2004/065101 is of a three-layer structure of main layer—core layer—main layer (for details, refer to its Examples). Since the core layer having a functional property is made of a material different from that of the main layer, the preforms had so far been limited to those of the two-kind-three-layer structure.
According to the technology of JP-B-6-49318, the shell layer-forming molten resin that is covering the core layer-forming molten resin like a shell, is fed into the inside of the main layer-forming molten resin that continuously flows through the outer flow path. Therefore, the preform that is formed is of a five-layer structure of main layer—shell layer —core layer—shell layer—main layer. The preform of a three-kind-five layer structure can be formed if the materials of the main layer, shell layer and core layer are changed. Though the technology of JP-B-6-49318 deals with a multi-kind-multi-layer structure, the core layer and the shell layer of a spherical shape requires a cumbersome operation for controlling the layer distribution of the multi-layer compression formed articles. Besides, difficulty is involved in wrapping the core layer with the shell layers.
The present invention was accomplished in view of the above circumstances, and its object is to provide a method of feeding a composite molten resin capable of easily forming a multi-kind-multi-layer preform and an apparatus therefor.